Despite many advances in assisted reproductive technology (ART), implantation rates are still low after controlled ovarian hyperstimulation (COH) and in vitro fertilization (IVF). It is assumed that two-thirds of implantation failures are associated with inadequate endometrium receptivity or with defects in the embryo-endometrium dialogue. The endometrium is receptive to blastocyst implantation during a spatially and temporally restricted window, called “the implantation window”. In humans, this period begins 6-10 days after the LH surge and lasts approximately 48 hours. Several parameters have been suggested for assessing endometrium receptivity, including endometrial thickness which is a traditional criterion, endometrial morphological aspect and endometrial and subendometrial blood flow. However, their positive predictive value is still limited.
More recently, transcriptomic approaches have been driven to identify bio-markers of the human implantation window. Using microarray technology in human biopsy samples, several authors have observed modifications in gene expression profile associated to the transition of the human endometrium from a pre-receptive (early-secretory phase) to a receptive (mid-secretory phase) state (Carson et al., 2002; Riesewijk et al., 2003; Mirkin et al., 2005; Talbi et al., 2006). However, among the various regulated genes, only two genes were in common between all these studies (Haouzi et al., 2009). Such variability in the results with the same approach may have several explanations: differences in the day of the endometrial biopsies, different patient profiles, and inadequate numbers of endometrial samples studied (n≦11). In addition, only one study compared the early and the mid-secretory phase in the same patient (Riesewijk et al., 2003), which seems to us a necessary condition to minimize the impact of inter-patient variability.
Therefore, there is still a need in the ART for reliable biomarkers of the human endometrium receptivity that will help improving the clinical outcome of IVF.